Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
  • H04W4/06—Selective distribution of broadcast services, e.g. multimedia broadcast multicast service [MBMS]; Services to user groups; One-way selective calling services
  • H04W4/10—Push-to-Talk [PTT] or Push-On-Call services
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W76/00—Connection management
  • H04W76/40—Connection management for selective distribution or broadcast
  • H04W76/45—Connection management for selective distribution or broadcast for Push-to-Talk [PTT] or Push-to-Talk over cellular [PoC] services
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
  • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
  • G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
  • G10L19/16—Vocoder architecture
  • G10L19/173—Transcoding, i.e. converting between two coded representations avoiding cascaded coding-decoding
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
  • H04W4/18—Information format or content conversion, e.g. adaptation by the network of the transmitted or received information for the purpose of wireless delivery to users or terminals
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
  • H04W88/18—Service support devices; Network management devices
  • H04W88/181—Transcoding devices; Rate adaptation devices

Definitions

• the technical field is wireless communications.
• the present invention relates to providing interoperability between wireless user devices that use different speech processing formats.
• An advantageous example application is Push-to-talk over Cellular (PoC) applications.
• Push-to-talk over Cellular provides a type of half-duplex or one ⁇ way communications service between two or more users. Users often form a group and then communicate with each other in a "point-to-multipoint" fashion. The communications are one-way: while one person (user) speaks, the others listen. A "turn" to speak is generally granted on a first come, first serve basis in response to user pressing a push to talk button on the user's wireless terminal/user equipment. PoC functionality is typically delivered across operator networks using Voice over IP (VoIP) protocols, although other technology implementations are possible.
• VoIP Voice over IP
• Push-to-talk over Cellular can be viewed as an IP Multimedia Subsystem
• PoC Session Initiation Protocol
• SIP Session Initiation Protocol
• FIG 2 illustrates an example communications protocol stack for PoC.
• the PoC application operates on an IP related stack that includes SIP, and Real-time Transport Protocol (RTP) is used to handle the voice packet delivery on the user plane.
• RTP Real-time Transport Protocol
• the SIP and RTP protocols employ the underlying User Data Protocol (UDP) and IP protocols that operate themselves on top of link layer (L2) and physical layer (Ll) protocols used in the cellular radio access network.
• UDP User Data Protocol
• L2 link layer
• Ll physical layer
• Figure 3 shows one example of mapping voice packets to a IP/UDP frame.
• the voice is divided into 20 msec speech encoded frames.
• the example speech encoding technique shown is adaptive multi-rate (AMR).
• AMR is a variable rate speech codec selected by the 3GPPP for 3G WCDMA cellular communications.
• ACELP Algebraic Code Excited Linear Predictive
• AMR provides toll quality sound at transmission rates from 4.75 to 12.2 Kbps.
• Multiple AMR frames are used to fill the AMR payload of the IP/UDP packet.
• the SIP protocol carries the Session Description Protocol (SDP) that is used to exchange session details between two PoC clients such as the type of media, codec, or sampling rate, etc.
• SDP Session Description Protocol
• This SDP information is carried by the SIP message in a way that is analogous to a document attachment being carried by an email message, or a web page being carried in an HTTP message.
• One SDP media capability that is exchanged during the voice communication session set-up is the speech codec supported by the PoC client and the media transport port(s) to be used for that speech codec.
• PoC is currently being standardized and agreed upon in the Open Mobile
• OMA Open Mobile Broadband Alliance
• 3GPP2 for CDMA2000 (IMT-2000) access technology
• 3GPP for WCDMA access technology each chose an appropriate speech codec for its respective organization that best suits its associated access technology.
• EVRC Enhanced Variable Rate Coder
• An EVRC codec is a Relaxation Code Excited Linear Prediction (RCELP) based codec and uses three rates: full rate at 8.5 kbps, half rate at 4 kbps, and eight rate at 800 bps and works with a 20 msec speech frame.
• RELP Relaxation Code Excited Linear Prediction
• One approach to provide interoperability is for the network infrastructure to support transcoding.
• a transcoder located in the PoC server would translate between different speech coding and decoding techniques. But the drawbacks with transcoding are substantial.
• transcoding between two low rate codec modes significantly reduces speech quality.
• transcoding operations between thousands of PoC clients would require powerful and expensive data processing resources in the PoC server.
• transcoding would likely increase end-to-end delay between the PoC clients reducing the quality of the PoC service.
• Another approach might be employ multiple codecs in each PoC client and PoC server to ensure a common codec. But here the cost is likely prohibitive ⁇ at least in a commercial context.
• Another interoperability problem is how to handle the use of different radio access bearers/transport formats. Even though two PoC clients may use the same "native" speech codec, those clients may use different radio access bearers for the PoC service.
• a 3GPP2 client terminal uses a "conversational class" bearer optimized for VoIP which produces a media stream with one EVRC full rate frame per IP packet.
• the other terminal may also be a 3GPP2 client terminal, but it uses a general purpose "interactive class" packet switched bearer, and thus would prefer media streams, (e.g., four EVRC frames per IP packet), to avoid unacceptable end-to-end media delay.
• a first wireless user communication device includes a primary speech codec that encodes a first speech message using a first speech encoding format.
• the encoded speech is then sent to a second wireless user communications device that includes a primary speech codec supporting a second speech encoding format.
• the first user device receives from the second user device a second speech message encoded using the second speech encoding format.
• the second speech message is then decoded by the first user device using a second speech decoder supporting decoding of the second speech encoding format.
• the first communication device does not support speech encoding using the second speech encoding format—regardless of whether the first communication device includes or does not includes an encoder for encoding speech using the first speech encoding format.
• the first speech message is transported using a first type of transport bearer that uses a first packetizing of speech encoded frames.
• the second speech message is transported using a second type of transport bearer that uses a second packetizing of speech encoded frames.
• the communication system includes a service support server for supporting the communication between the first and second devices. The server re-packetizes at least a portion of the first speech message before the first speech message is sent to the second wireless communication device.
• the first user device sends the service support server a signaling message that includes one or more attributes indicating that the first user device supports speech encoding and decoding using the first speech encoding format and decoding of speech encoded using the second speech encoding format, but does not support encoding speech using the second speech encoding format.
• the signaling message preferably also includes one or more attributes indicating that the first wireless user communication device supports a first transport bearer format for speech encoded using the first speech encoding format and a second transport bearer format for speech encoded using the second speech encoding format.
• the first and second wireless user communications devices are Push-to-talk (PTT) type communications devices.
• PTT communication is a PTT over Cellular (PoC) communication.
• FIGURE 1 is an illustration of a Push-to-talk over Cellular (PoC) group call
• FIGUPvE 2 is an example communications protocol stack for PoC communications ;
• FIGURE 3 shows multiple speech codec frames packed into a frame
• FIGURE 4 is a function block diagram of a PoC client
• FIGURE 5 is a diagram of PoC clients communicating in a PoC call using different access networks with different codecs and different bearer or transport formats;
• FIGURE 6 is diagram of an interoperability solution for PoC clients communicating in a PoC call using different access networks with different codecs and different bearer or transport formats;
• FIGURE 7 is a flowchart illustrating example, non-limiting procedures for a PoC client from Figure 6;
• FIGURE 8 is a flowchart illustrating example, non-limiting procedures for a PoC server from Figure 6;
• FIGURE 9 is a a PoC call set example.
• wireless clients communicate using a radio access network over a wireless interface.
• Non-limiting examples of tow different access network technologies include a UMTS (Universal Mobile Telecommunications System) and an ! IMT-2000 (International Mobile Telecommunications 2000) system.
• the UMTS system includes one or more core networks coupled to a radio access network called a UTRAN : which means UMTS Terrestrial Radio Access Network.
• the UTRAN includes one or - more radio network controllers (RNCs) coupled to one or more base stations sometimes referred to as Node-B's.
• the radio access network communicates with multiple user equipments (UEs) over a wireless interface.
• UEs user equipments
• a UE includes but is not limited to a subscriber terminal, a mobile terminal, a mobile phone, a cell phone, a mobile station, a wireless terminal, etc., and includes any terminal having a speech communication capability.
• the user equipment may be a terminal (such as a personal computer PC) having Internet access and VoIP capability for voice communication over the Internet.
• PoC client 10 An example of a possible implementation of user equipment configured for PoC communications is a PoC client 10 illustrated as a simplified block diagram in FIG. 4.
• Radio transceiving circuitry 14 is coupled to an antenna 16 and a controller 12.
• the controller 16 includes baseband signal processing 28 which performs any kind of baseband signal processing required in any specific implementation, such as an analog- digital (A/D) conversion of analog speech signals from a microphone (not shown), voice encoding, IP packet building, frame building, de-framing, IP packet de-building, voice decoding, and digital-analog (D/ A) conversion of a received digital speech signal into an analog signal applied to a loudspeaker (not shown).
• the voice coder and decoder are often referred to as a codec which performs speech compression/decompression and error detection/correction coding/decoding. Different codecs use different compression/decompression algorithms and usually provide different coding/decoding rates.
• the controller 12 includes PoC client communications application software 24 and other applications software 26.
• the controller 12 further controls signaling, both out-band (e.g., SIP) and in-band or embedded, as well as IP packet building and de-building.
• the start and stop of a speech message is set by a PTT button or switch 18 coupled to the controller 12, which can be replaced by any user-operated device, such as a voice activity detector (VAD).
• a user interface may include a display 22 and a keyboard 20 coupled to the controller 12.
• the PoC client application 24 provides the PoC communication service.
• the client application 24 maintains group information, such as group identification information and group membership information.
• group information such as group identification information and group membership information.
• the communication client 24 may also provide tools for group creation, for attaching to (joining) a group and for detaching from (leaving) the group, obtaining "floor" control, starting and ending a speech message, etc.
• FIG. 5 illustrates an example diagram 30 of PoC clients communicating in a PoC call using different access networks with different codecs and different bearer/transport formats.
• the wireless PoC client A 32 includes a codec of type A and uses a radio access bearer of type A or transport format of type A.
• Codec A uses a certain type of speech compression/decompression algorithm and employs various coding rates.
• Example speech different compression/decompression algorithms include CELP, ACELP, RCELP, and extended CELP.
• Examples of different radio access bearer types/transport format types used in 3GPP include conversational class, interactive class, streaming class, and background class.
• Radio access-bearer (RAB) service attributes which can be used to differentiate the management of radio access bearers within the UMTS Terrestrial Radio Access Network (UTRAN), have also been defined and include: traffic class, maximum bit rate, guaranteed bit rate, delivery order, maximum Service Data Unit (SDU) size, SDU format information, SDU error ratio, residual bit error ratio, delivery of erroneous SDUs, transfer delay, traffic handling priority (THP), allocation and retention priority, source statistics descriptor, and signaling indication.
• SDU Service Data Unit
• TCP traffic handling priority
• TCP traffic handling priority
• source statistics descriptor source statistics descriptor
• the wireless PoC client B 40 is coupled to the PoC server 36 via an access network B 38 and includes a codec of type B and uses a radio access bearer of type B or transport format of type B.
• the wireless PoC client C 44 is coupled to the PoC server 36 via access network C 42 and includes a codec of type C and uses a radio access bearer of type C or transport format of type C.
• Each codec A, B, and C uses a different type of speech compression/decompression algorithm with different coding rates and different bearer/transport formats. Absent some interoperability mechanism, the different codecs and different bearer transport formats prevent PoC communications between the PoC clients.
• SIP and SDP are used for signaling.
• the most important method in SIP is the INVITE method used to establish a session between participants.
• a session is a collection of participants, and streams of media between them, for the purposes of communication.
• a UE initiates a PoC call by generating an initial INVITE request.
• Session Description Protocol SDP
• the first sub-field is the media type. Currently defined media include: "audio”, "video”, “application”, “data” and “control”.
• the second sub-field is the transport port to which the media stream will be sent. TCP/IP transport layer addressing is accomplished using TCP and UDP ports.
• Each port number within a particular IP device identifies a particular software process.
• RTP/AVP 31 specifies that ports 49170 and 49171 form one RTP/RTCP pair and 49172 and 49173 form the second RTP/RTCP pair.
• RTP/AVP is the transport protocol and 31 is the format.
• the third sub-field is the transport protocol.
• the fourth and subsequent sub-fields are media formats.
• the 3GPP2 community has chosen EVRC as its mandatory speech codec, that PoC user A uses a 3GPP2 PoC client A, and that PoC client A uses an IP-only radio access bearer called Service Option 33 (SO33).
• PoC user B uses a 3GPP2 terminal called PoC client B and a.radio access bearer optimized for VoIP called Service Option 60 (SO60).
• AMR as its mandatory speech codec
• PoC user C uses a 3GPP terminal called PoC client C
• PoC client C is a GSM phone using AMR5.15 as default speech codec mode.
• the problem then is how to achieve interworking between PoC client A, PoC client B, and PoC client C.
• Each PoC client has only one "native" speech codec implemented.
• This native speech codec contains both an encoder and a decoder.
• the native speech codec is an AMR codec if the PoC client is implemented on a 3GPP terminal or an EVRC codec if the PoC client is implemented on a 3GPP2 terminal.
• each PoC client includes one or more other secondary or non-native speech decoders that provide interoperability with non-native speech codecs. So to achieve interoperability in the example above, the 3GPP terminal also includes a secondary or non-native EVRC speech decoder, and the 3GPP2 terminal also includes a secondary or non-native AMR speech decoder.
• the PoC client uses the native speech codec for speech encoding and decoding. But the PoC client can also decode speech from another PoC client's native speech codec, regardless of what type of native speech codec the other PoC uses, using an appropriate non-native speech decoder.
• the PoC client does not support encoding speech using a non-native speech encoder or encoding format. This means the PoC client either cannot perform non-native speech encoding or is configured not to perform non-native speech encoding even though the PoC client may have the ability to perform non-native speech encoding. This may result in "asymmetrical encoding.” In the example, AMR encoded bits are sent in one direction of the conversation while EVRC encoded bits are sent in the other direction.
• a non-native speech decoder can be implemented as a software decoder running on a microprocessor rather than a hardware-based decoder, e.g., a DSP.
• the non-native speech decoder may also be implemented use a native codec DSP. Since PoC is a half duplex service, the additional speech decoder can be loaded into the DSP during reception of speech while the native speech codec is loaded into the DSP while encoding speech
• the SDP message above indicates support for speech codecs AMR, G723 and G729 all on transport port 62986.
• the native speech codec is given a certain transport port denoted for example by port X.
• Each additional speech decoder is given a transport port different from the native speech codec. In this example, the additional speech decoder is denoted by port Y.
• the receiving PoC client receives native speech codec data on one transport port (port X) and the non-native speech coded data on another transport port (port Y). Consequently, the receiving PoC client's non native speech coded data may be transported over a radio access bearer using one type of transport format, while native speech coded data may be transported over another radio access bearer using another type of transport format.
• the PoC client may signal its native speech codec using more than one m- line in SDP (using different transport ports). This indicates that the speech codec may be used with different settings when used over different radio bearers.
• the PoC server re-packetizes the speech coded frames. Re-packetization describes changing packets from one packet-format to another packet format without modifying the actual speech information bits, e.g., the payload is not changed.
• An example is changing packets between header-less and interleaved/bundled packets formats.
• one PoC client on a 3GPP2 terminal may use a radio access bearer optimized for VoIP called Service Option 60 (SO60) and thus use a header-less packet format.
• Another 3GPP2 PoC client may use an IP-only radio access bearer called Service Option 33 (SO33) and an interleaved/bundled packet format. To ensure interoperability, the PoC server re-packetizes between these two packet formats.
• SO60 radio access bearer optimized for VoIP
• the PoC clients may use frame bundling which means that more than one speech coded frame is sent per IP packet (see the example of frame bundling shown in Figure 3).
• the number of speech frames per IP packet is signaled using the SDP 'ptime' attribute.
• the server may have to re-packetize the speech frames according to the agreed ptime or re-negotiate the ptime attribute, i.e., user plane adaptation, which is a slower process than re-packetization.
• the PoC server must perform re-packetizing since the client negotiates a desired ptime attribute to the limitations of the negotiated radio bearer.
• Frame packetization is used to reduce the media bit rate in the absence of header compression. If this example. If a codec produces a 5 kbps media stream and the IP overhead for one 20 msec codec frame is about 16 kbps, the total IP bit rate is about 21 kbps. But if four frames are packetized per IP packet, the total IP bit rate goes down to about 9 kbps. In that case, a 10 kbps radio bearer may be used.
• ptime together with the codec mode indicate the downlink throughput to the UE, thereby defining the bit rate at which the UE can receive data. If the PoC server receives a data stream that uses a higher bandwidth than that downlink bandwidth, the PoC server must re-packetize.
• the PoC client A 52 includes non-native speech decoders B 62 and C 64 in addition to its native speech codec A 60.
• the PoC client A sends a SIP/SDP setup message that specifies the native codec, the supported non-native speech decoder(s), and the corresponding transport ports and radio access bearers/transport formats.
• the PoC client A is coupled to the PoC server 54 that includes a PoC server application 66 and a re-packetizer 68. Also coupled to the PoC server 54 are PoC clients B 56 and C 58.
• the PoC client B includes non-native speech decoders A 72 and C 74 in addition to its native speech codec B 70.
• the PoC client B sends a SIP/SDP setup message that specifies the native codec, the supported non-native speech decoders, and the corresponding transport ports and radio access bearers/transport formats.
• PoC client C includes non-native speech decoders A 78 and B 80 in addition to its native speech codec C 76.
• the PoC client C sends a SIP/SDP setup message that specifies the native codec, the supported non-native speech decoders, and the corresponding transport ports and radio access bearers/transport formats.
• FIG. 7 is a flowchart that illustrates non-limiting example procedures followed by a PoC client for a PoC session setup that permits interoperabililty with other PoC clients that have different speech processing and transport formats.
• the PoC client may initiate the PoC session, e.g., a group call (step Sl).
• the PoC client formulates and includes in the SIP signaling to the PoC server and SDP message indicating the native preferred speech codec, non-native speech decoding supported, and transport formats supported for the native codec and non-native decoder(s) (step S2).
• the PoC server acknowledges that message with the PoC client (step S3).
• the call commences, and speech traffic is encoded and communicated, e.g., to the group (step S4).
• FIG 8 is a flowchart that illustrates non-limiting example procedures followed by a PoC server for a PoC session setup that permits interoperabililty between PoC clients that have different speech processing and transport formats.
• a PoC client PoC session request e.g., for a group call, is received (step SlO).
• the PoC server receives from each PoC client an SDP message that indicates the native speech codec, non-native speech decoding supported, and transport formats supported for the native codec and non-native decoder(s) (step S12).
• the PoC server acknowledges that message with the PoC client and sets up the requested session (step S 14).
• the call commences, and speech traffic is encoded and communicated, e.g., to the group.
• the PoC server re-packetizes received IP packets to accommodate different transport formats and codec coding rates between the PoC clients (step S 16).
• FIG. 9 shows specific PoC call setup SIP/SDP messages sent to the PoC server 54.
• the use of the 'sendrecv' attribute indicates the preferred native speech codec.
• AMR 'sendrecv
• the use of the 'sendrecv' attribute indicates the preferred native speech codec.
• the PoC client A user activates PTT to send a talk burst 1 to the group.
• Talk burst 1 is encoded using EVRC and is sent using the interleaved/bundled packet format over SO33 to the PoC server 54 via PoC client A's access network(s).
• the PoC server 54 determines if the PoC client B should receive it over an SO60 bearer using the header-less packet format or over an SO33 bearer using the interleaved/bundled packet format.
• the PoC server 54 performs re-packetizing from the interleaved/bundled packet format to the header-less packet format if needed.
• the talk burst 1 is decoded in the PoC client B using its non-native EVRC decoder.
• the PoC server 54 forwards the talk burst 1 to PoC client C using the interleaved/bundled packet format over an interactive or a streaming packet switched bearer.
• the PoC server 54 performs re-packetizing if the ptime attribute indicates need for re-packetizing.
• the talk burst is decoded in the PoC client C.
• the PoC client B sends a talk burst 2.
• Talk burst 2 is encoded using its native EVRC codec and is sent using the header-less packet format over SO60 to the PoC server 54.
• the PoC server 54 forwards the talk burst to PoC client A using the interleaved/bundled packet format over SO33 after re-packetizing the EVRC frames from header-less to interleaved/bundled packet format.
• the talk burst 2 is decoded in the PoC client A using its native EVRC codec.
• the PoC server 54 forwards the talk burst to PoC client C using the interleaved/bundled packet format over an interactive or a streaming packet switched bearer.
• the PoC server 54 must re-packetize the EVRC frames (from header-less to interleaved/bundled packet format).
• the talk burst is decoded in the PoC client C using its non-native EVRC decoder.
• the PoC client C sends a talk burst 3 using its native AMR codec.
• Talk burst 3 is encoded using AMR, and the PoC client C must chose the default AMR mode (here AMR5.15).
• the AMR frames are sent bundled (4 frames per packet) using an interactive or a streaming packet switched bearer.
• the PoC server 54 forwards the talk burst 3 to PoC client A over SO33 after re-packetizing if the ptime attribute indicates the need for re-packetizing.
• the talk burst is decoded in the PoC client A using it non-native AMR decoder.
• the PoC server 54 forwards the talk burst 3 to PoC client B over SO3 after re-packetizing if the ptime attribute indicates a need.
• the talk burst 3 is decoded in the PoC client B using it non-native AMR decoder.
• a PoC client may include multiple codecs but nevertheless may use this kind of SIP/SDP message to indicate that the preferred codec may only be used to encode speech and that the other codec(s) will only be used for speech decoding of speech encoded using a non-preferred speech encoding format.
• codecs may be listed in a preferred order. For example, a different low complexity default codec, e.g., a G.711 sendrecv could be listed before EVRC recvonly .
• the interoperability technology described above provides interoperability between different UEs that have different speech processing configurations and capabilities.
• Speech decoders usually have lower complexity then speech encoders and therefore need less "computing power.” Accordingly, the speech decoder can use an "all- purpose" CPU rather than a DSP. And a service provider can readily offer interoperability by provisioning clients with a new decoder when needed.

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